If you’ve ever been scared by the prospect of visiting underground caverns, cracks, and wells, you have a good reason to be. Not only do you have to worry about the possibility of the walls caving in, trapping you underground until you eventually run out of oxygen...but if you ever fall victim to a serial killer, you may just end up in one of these places. These holes have dark pasts. And I’m not talking about the lack of sunlight.